Complexing resins and method for preparation thereof

ABSTRACT

The invention provides a process for preparing polymeric beads of complexing resin incorporating magnetic particles, which process comprises: producing a dispersion having a continuous aqueous phase and a dispersed organic phase, said organic phase comprising one or more polymerisable monomers, magnetic particles and a dispersing agent for dispersing said magnetic particles in the organic phase; polymerising said one or more polymerisable monomers to form polymeric beads incorporating said magnetic particles, wherein said polymeric beads include amine groups capable of complexing a transition metal cation, or wherein said polymeric beads are reacted with one or more compounds to provide amine groups capable of complexing a transition metal cation, complexing resins prepared by this process, and polymeric beads of complexing resin comprising a polymer matrix having magnetic particles dispersed substantially uniformly therein, wherein the polymer matrix incorporates amine groups capable of complexing a transition metal cation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing of PCT/AU03/00015 under 35U.S.C. 371 which claims priority to Australian Patent ApplicationPR9878/02 filed 8 Jan. 2002, both of which are incorporated in theirentirety herein to the extent not inconsistent herewith.

The present invention relates to complexing resins and in particular, topolymeric beads of complexing resin incorporating magnetic particles andprocesses for their preparation. The invention further relates to amethod of separating transition metals from aqueous solutions using thecomplexing resin.

Ion exchange is widely used as a technique for removing both organic andinorganic species from water. Ion exchange techniques conventionallyinvolve passing water through a packed bed or column of ion exchangeresin. Target species are removed by being adsorbed on to the ionexchange resin. Ion exchange resins are commonly used for removingcontaminants from water.

Industrial wastewaters and mine drainage, etc, are often contaminatedwith dissolved transition metal salts. Such metal contaminants must beremoved before the water can be released to the environment because ofthe toxic effect most transition metals have on human beings and otherliving species. Increasingly, groundwater is becoming contaminated withtransition metal compounds and requires similar treatment to comply withpotable water guidelines. In such instances transition metalcontaminants are typically removed by precipitation with lime, causticsoda, sodium sulfide, or similar reagents. However, this process yieldsa voluminous sludge that must be dewatered and disposed of in a securelandfill.

Ion exchange would be preferable to precipitation because it couldrecover the transition metal salts as an aqueous concentrate, whichcould potentially be recycled to a beneficial use. However, effectiveuse of commercial ion exchange resins in such applications is currentlynot viable. In particular, most commercial resins are too slow tofunction effectively at short contact times. Treating substantial flowsof water or liquid at adequate contact times requires very large columnsand is therefore not economically feasible. Also, commercial resinstypically have a poor capacity utilisation due to their low selectivityfor transition metals over ever-present innocuous background ions.

Ion exchange resins incorporating dispersed magnetic particles have beendescribed as suitable for applications involving continuous high flows.In the absence of shear, attraction between the magnetic particles inthe resin causes the resin beads to flocculate and settle rapidly,enabling such resins to be readily separated under demanding processconditions. For such resins to operate effectively, the magneticmaterial should be incorporated in a manner that prevents its loss byerosion or dissolution during use. For this reason it is highlydesirable that the magnetic material should be dispersed evenlythroughout the polymeric bead. Improved mechanical strength is a furtherbenefit of even particulate dispersion.

Processes for the manufacture of magnetic ion exchange resins have beendescribed in some prior art patents. For example, U.S. Pat. No.2,642,514, discloses an ion exchange process using a mixed ion exchangeresin. One of the ion exchange resins is a magnetic resin. The magneticresin is produced by polymerising a reagent mix until a viscous syrup isobtained. Magnetite is added to the viscous syrup and the mixture isagitated to mix in the magnetite. The mixture is cured to form a hardresin that is subsequently ground to form irregular particles ofmagnetic resin.

European Patent Application No. 0,522,856 also discloses the manufactureof magnetic ion exchange resins by grinding or crushing a polymer havingmagnetite dispersed throughout the polymer matrix. The processes forproducing magnetic ion exchange resins disclosed in U.S. Pat. No.2,642,514 and EP 0,522,856 require a grinding step, which increases thecost and complexity of the process and increases losses due to theformation of polymer particles outside the desired particle size rangeduring the grinding step. Further, the ground particles are irregular inshape and easily abraded.

An alternative process for producing magnetic ion exchange resins isdescribed in Australian Patent Application No. 60530/80. In thisprocess, magnetic porous crosslinked copolymer particles are produced bya suspension polymerisation process. A mixture of polymerisable vinylcompounds, magnetic powder, polymerisation initiator and dispersionstabiliser is dispersed in water and polymerised.

A similar process for producing magnetic ion exchange resins isdescribed in Japanese Patent Application No. 62141071. In this processan electron donor substance such as polyvinyl pyridine-styrenecopolymer, polyacrylamide-styrene copolymer or polyvinyl imidazolecopolymer is preferably added to the mixture in order to stabilise thedispersion of magnetic powder. According to the specification, thedispersion treatment is important for stabilising the dispersed state sothat the rate of settling of the magnetic powder is reduced by breakingup magnetic particles which have clumped together in secondary or largerparticles into primary particles. Furthermore, it is necessary to usedispersion equipment which differs from normal mixing equipment, withspecial mixers being required.

Many of the aforementioned difficulties associated with producingmagnetic ion exchange resins can be overcome by using the processdisclosed in Australian patent No.704376. This patent describes anaqueous suspension polymerisation process which involves polymerising adispersed organic phase comprising monomer, magnetic powder and adispersing agent. During polymerisation the dispersing agent reacts withmonomer to become covalently bound within the resin. By this process,spherical polymeric beads having an even distribution of magnetic powderthroughout can be produced. The patent indicates that resins suitablefor separating transition metals can be prepared by hydrolysis ofpoly(ethyl acrylate) beads, thereby providing a weak acid cationexchange resin.

While providing an effective process to prepare magnetic ion exchangeresins, the resins contemplated in Australian patent No.704376 are notparticularly suitable for use in separating transition metals fromaqueous solutions as they would have poor capacity utilisation due totheir low selectivity for transition metals over innocuous backgroundions.

Commercial weak base resins, usually used as anion exchangers, providemeans for the selective adsorption of transition metal salts overinnocuous background ions, for example alkali and alkaline earth metalssuch as Na⁺, Ca²⁺ or Mg²⁺, when used as complexing resins, in their freebase form. However, such resins are not suited to continuous high flows.In particular, the resins would be difficult to recover from the treatedwater and their large size, typically 0.5-1.2 mm, provides a relativelyslow adsorption rate, especially at low ion concentrations.

Accordingly, there is a need to develop complexing resins that areparticularly suited to selectively removing transition metals fromcontinuous high flows.

According to a first aspect the present invention provides a process forpreparing polymeric beads of complexing resin incorporating magneticparticles, which process comprises: producing a dispersion having acontinuous aqueous phase and a dispersed organic phase, said organicphase comprising one or more polymerisable monomers, magnetic particlesand a dispersing agent for dispersing said magnetic particles in theorganic phase; polymerising said one or more polymerisable monomers toform polymeric beads incorporating said magnetic particles, wherein saidpolymeric beads include amine groups capable of complexing a transitionmetal cation, or wherein said polymeric beads are reacted with at leastone or more compounds to provide amine groups capable of complexing atransition metal cation.

In a second aspect the present invention provides polymeric beads ofcomplexing resin comprising a polymer matrix having magnetic particlesdispersed substantially uniformly therein, wherein the polymer matrixincorporates amine groups capable of complexing a transition metalcation.

The process of the present invention advantageously provides the abilityto form spherical polymeric beads of complexing resin that have magneticparticles which are substantially evenly distributed throughout thepolymeric beads. In addition, the present invention provides for thepreparation of polymeric beads comprising complexing amine groups whichare suitable as complexing resins and demonstrate an ability toselectively remove transition metals from aqueous solutions in thepresence of innocuous background ions under continuous high flowconditions.

In accordance with the process of the present invention the organicphase is the dispersed phase. The organic phase includes one or morepolymerisable monomers that polymerise to form the polymer matrix of thepolymeric beads. It is preferred that the polymer matrix is a copolymerbased on two (or more) monomers. Generally the polymeric beads will beprepared from two types of polymerisable monomers:

-   -   (a) crosslinking monomers which are able to provide crosslink        points; and    -   (b) functional monomers which are able to provide functional        groups.

By the process of the invention, the organic phase preferably includescrosslinking monomers and functional monomers. Some monomers, such asbis(diallylamino)alkanes or bis(acrylamidoethyl)amine can function asboth crosslinking monomers and functional monomers. The functionalmonomers may be amine functionalised polymerisable monomers that providethe necessary amine groups to enable the polymeric beads to act as acomplexing resin. The functional monomers may provide polymeric beadswith sites that can be later reacted with one or more compounds toprovide the necessary amine groups that will enable the polymeric beadsto act as a complexing resin. The polymer matrix of the beads may be acopolymer matrix. Accordingly, other monomers may be included in theorganic phase to copolymerise with the crosslinking monomers and thefunctional monomers, for example backbone monomers may be included.

The cross-linking monomers may be selected from a wide range ofmonomers, including divinyl monomers such as divinyl benzene,ethyleneglycol dimethacrylate or poly(ethyleneglycol) dimethacrylate ormethylene bisacrylamide, ethyleneglycol divinylether and polyvinyl estercompounds having two or more double bonds, such as trimethylolpropanetriacrylate or trimethacrylate. This list is not exhaustive.

A wide range of functional monomers may also be used in the process ofthe present invention. Suitable monomers include glycidyl methacrylate,vinyl benzyl chloride, methyl acrylate, N-vinyl formamide,dimethylaminoethyl methacrylate, aminopropyl acrylamide andmethacrylamide, N,N-dimethylaminopropyl acrylamide and methacrylamide,vinyl pyridine and organic-soluble diallylamine or vinylimidazole salts.This list is not exhaustive.

The backbone monomers include any monomer polymerisable by free radicalssuch as styrene, vinyl toluene, methyl methacrylate and other acrylatesand methacrylates. This list is not exhaustive.

In order to increase the efficiency of removal of transition metals fromwater being treated by the complexing resin, it is preferred that thepolymeric beads are macroporous. This increases the total surface areaof each bead available for contact. To produce macroporous polymericbeads according to the present invention, the dispersed phase shouldinclude one or more porogens. The porogen becomes dispersed throughoutthe droplets that form the dispersed phase, but the porogen does nottake part in the polymerisation reaction. Accordingly, after thepolymerisation reaction is completed, the porogen can be removed fromthe polymeric beads, for example by washing or steam stripping, toproduce macroporosity in the polymeric beads.

Suitable porogens for use in the process of the present inventioninclude aromatic compounds such as toluene and benzene, alcohols such asbutanol, iso-octanol, cyclohexanol, dodecanol, isoamyl alcohol,tert-amyl alcohol and methyl iso-butyl carbinol, esters such as ethylacetate and butyl acetate, saturated hydrocarbons such as n-heptane,iso-octane, halogenated solvents such as dichloroethane andtrichloroethylene, plasticisers such as dioctylphthalate and dibutyladipate, polymers such as polystyrene and polyvinyl acetate; andmixtures thereof. Mixtures of cyclohexanol with other porogens such asdodecanol or toluene have been found to be especially suitable for useas a porogen in the process of the present invention. It will beappreciated that the above list of porogens is not exhaustive and thatthe invention encompasses the use of other porogens and othercombinations of porogens.

Incorporation of magnetic particles into the polymeric beads results inthe beads becoming magnetic. Magnetic separation techniques may be usedto conveniently separate the beads from a solution or liquid beingtreated. The magnetic particles used in this embodiment of the presentinvention may be any solid material that is magnetic. Examples includeγ-iron oxide (γ-Fe₂O₃, also known as maghemite), magnetite (Fe₃O₄),chromium dioxide, other metal oxides and more exotic magnetic materials,such as those based on neodymium or samarium and other rare earthmaterials, for example samarium-cobalt or neodymium iron boride.Maghemite is especially preferred because it is inexpensive.

The magnetic material is added during the process in the form ofparticles and it may or may not be magnetised upon addition. Theparticle size of the particles may range up to a size that is up toone-tenth of the particle size of the polymeric beads formed in theprocess of the present invention. Particles that are larger than thatmay be difficult to evenly disperse into the polymeric beads. Morepreferably, the particles of magnetic material range in size fromsub-micron (e.g. 0.1 μm) to 500 μm, most preferably from 0.1 μm to 10μm.

The process of the present invention includes a dispersing agent fordispersing the magnetic particles in the dispersed phase. The dispersingagent acts to disperse the magnetic particles in the droplets of thedispersed phase to thereby form a stable dispersion (or suspension) ofthe magnetic particles in the dispersed phase. The dispersing agent alsoacts to promote a substantially even distribution of magnetic particlesthroughout the resultant polymeric beads. In this regard, the problem oferosion of the magnetic particles from the polymeric beads in service,as may happen if the magnetic particles were located only on the outersurface of the beads is avoided, or at least alleviated. Suitabledispersing agents will generally have a good binding affinity toward thesurface of the magnetic particles and preferably should be able tochemically bond to the surface of the particles. The dispersing agentwill also generally be soluble in the one or more polymerisablemonomers. Preferably, the dispersing agent reacts with one or more ofthe monomers to become covalently bound within the polymer matrix. Useof a dispersing agent of this type not only results in a substantiallyeven distribution of magnetic particles throughout the polymeric bead,but the particles also advantageously become more effectively boundwithin the bead through the dispersing agent being covalently bound tothe polymer matrix. In this case, the problem of leaching of themagnetic particles from the polymeric beads can be avoided, or at leastalleviated. Selection of the dispersing agent will typically depend uponthe particular magnetic material and monomers being used. Personsskilled in the art should be able to readily select a suitabledispersing agent having regard to the specific reaction system employed.

The polymerisation reaction that takes place in the process of thepresent invention is a suspension polymerisation reaction and techniquesknown to those skilled in the art to control and monitor such suspensionpolymerisation reactions apply to the present invention. In order tomaintain the dispersed phase in the form of a suspension of droplets inthe continuous phase whilst avoiding aggregation of the droplets, astabilising agent is preferably used. Suitable stabilising agents mayinclude polyvinyl alcohol, polyvinyl pyrrolidone, gelatine, methylcellulose or sodium polyacrylate. It is to be understood that theinvention extends to cover any stabilising agent that may be suitablefor use. The stabilising agent is typically present in an amount of 0.01to 5% by weight, and preferably 0.05 to 2% by weight, based on theweight of the whole mixture.

It will also be generally necessary to use an initiator to initiate thepolymerisation reaction. The initiator to be used depends upon themonomers present in the reaction mixture and the choice of initiator andthe amount required will be readily apparent to the skilled addressee.By way of example only, suitable initiators include azoisobutyronitrile,benzoyl peroxide, lauroyl peroxide and t-butyl hydroperoxide. The amountof initiator used is generally in the range of 0.01 to 5 wt %, morepreferably 0.10 to 1%, calculated on the total weight of monomer(s).

In a preferred embodiment of the present invention, the monomer mixturemay include a functional monomer present in an amount of from 10 to 99%by weight, based upon the weight of total monomers, more preferably 50to 90% by weight (same basis). The crosslinking monomers may be presentin an amount of from 1 to 90% by weight, based on the weight of totalmonomers, more preferably 10 to 50% by weight (same basis). Additionalmonomers may be present in an amount of 0 to 60% by weight, morepreferably 0 to 30% by weight, based on the weight of total monomers.The total monomers may constitute from 1 to 50%, more preferably 5 to30% by weight of the whole suspension polymerisation mixture.

The magnetic particles are preferably added in an amount of from 10 to300 wt %, based on the weight of total monomers, more preferably 20 to100% by weight (same basis). The dispersing agent is preferably added inan amount of 0.10 to 30% by weight, more preferably 1 to 10% by weight,based on the weight of magnetic particles.

The dispersion of the dispersed phase (which includes the monomer(s)) inthe continuous phase is usually achieved by mixing the organic andaqueous phases and shearing the resulting mixture. The shear applied tothe dispersion can be adjusted to control the size of the droplets ofthe dispersed phase. As the droplets of dispersed phase are polymerisedto produce the polymeric beads, the shear applied to the dispersionlargely controls the particle size of the polymeric beads. Generally,the polymeric beads are controlled to have a particle size in the rangeof 10-5000 μm.

Once a stable dispersion of dispersed phase in continuous phase isestablished, the polymerisation reaction is started by heating thedispersion to the desired reaction temperature. The dispersion may beheld at the desired reaction temperature until the polymerisationreaction is substantially complete.

Depending upon the monomers used, once the polymerisation is complete,the resulting polymeric beads may include amine groups that will enablethe polymeric beads to act as a complexing resin, the amine groups beingprovided by the polymerised residues of one or more of the functionalmonomers. Functional monomers capable of introducing amine functionalityto the beads include, but are not limited to, dimethylaminoethylmethacrylate, aminopropyl acrylamide and methacrylamide,N,N-dimethylaminopropyl acrylamide and methacrylamide, vinyl pyridine,organic-soluble diallylamine or vinylimidazole salts.

Alternatively, once the polymerisation is complete, the resultingpolymeric beads may require subsequent treatment to provide the aminegroups that will enable the polymeric beads to act as a complexingresin. The particular treatment process used will be dependent on thecomposition of the polymeric beads to be treated. Generally, thetreatment process will involve reacting the polymeric beads with one ormore compounds that convert functional groups present on the beads toamine groups or reacting functional groups on the beads with one or morecompounds that introduce amine groups to the beads.

In the treatment process where functional groups on the beads areconverted to amine groups, various combinations of suitable functionalgroups and reactants may be employed, the nature of which would be knownto those skilled in the art. It is preferable that the functional groupson the beads are amide groups and more preferable that the amide groupsare introduced to the polymeric beads by way of an amide functionalmonomer. Exemplary amide functional monomers include, but are notlimited to, N-vinyl formamide or N-methyl-N-vinyl acetamide. Amidegroups can be readily converted to amine groups by hydrolysis, Hofmanndegradation or borohydride reduction, hydrolysis is a preferredtechnique. For example, amide groups in N-vinylformamide orN-methyl-N-vinylacetamide monomer units can be converted to amine groupsby hydrolysis.

In the treatment process where functional groups on the beads arereacted to introduce amine groups, various combinations of suitablefunctional groups and reacting compounds may be employed, the nature ofwhich would be known to those skilled in the art. Preferred functionalgroups on the beads include, but are not limited to, halogens, epoxides,esters and amides. It is preferable that such functional groups areintroduced to the polymeric beads by way of appropriate functionalmonomers. Exemplary functional monomers in this regard include, but arenot limited to, vinyl benzyl chloride, glycidyl methacrylate, acrylateor methacrylate esters or amides. Such functional groups can be reactedwith compounds that introduce amine groups. Suitable compounds include,but are not limited to, amines, diamines, and polyamine compounds andtheir respective salts. Preferred compounds for introducing amine groupsinclude, but are not limited to, piperidine, N,N-diethylethylenediamine, dimethylamine, diethylamine, dimethylaminopropylamine,ethylenediamine, diethylenetriamine, polyethyleneimine and theirrespective salts.

The complexing properties of the polymeric beads will be primarilydictated by the nature of the amine groups present therein. Such aminegroups should be readily accessible to undergo complexation withtransition metal cations. It will be appreciated by those skilled in theart that amine groups to be included in the polymeric beads, either bydirect polymerisation or by subsequent treatment, have little or noaffinity to complex with alkali and alkaline earth metal cations, butcan readily complex with transition metal cations. Those skilled in theart will also appreciate that the selection of amine groups to beincluded in the polymeric beads will be dependent on both the nature ofthe species to be separated and the nature of background ions present inthe solution. For example, selectivity may be affected by factors suchas steric crowding of the nitrogen atoms, electron density on thenitrogen atoms and the availability of multiple nitrogen atoms to formchelate complexes.

The beads may require cleaning prior to a subsequent treatment or priorto being used. This may be achieved by a sequence washing steps or bysteam stripping the beads.

One method for cleaning the polymeric beads includes the followingsteps:

-   -   (a) add reaction product to a large excess of water, stir and        allow to settle;    -   (b) separate beads from the supernatant;    -   (c) add separated beads to a large excess of water, stir and        allow to settle before separating beads from the supernatant;    -   (d) repeat step (c) several times;    -   (e) disperse water washed beads in alcohol (ethanol);    -   (f) separate beads from alcohol and dry.

An alternative clean-up procedure is to steam strip the porogens andthen wash the polymeric beads to remove any free solid particulatematerial.

In an especially preferred embodiment of the invention the polymericbeads are formed as a copolymer of glycidyl methacrylate and divinylbenzene. The monomers reside in the organic phase, which also includes amixture of cyclohexanol with toluene or dodecanol as porogens. Polyvinylalcohol is used as a stabilising agent. A free radical initiator such as“VAZO” 67 or Azoisobutyronitrile (AIBN) is added to the organic phase asa polymerisation initiator and γ-iron oxide is the magnetic material.The solid phase dispersing agent preferred for use in this system is ablock copolymer of poly(hydroxystearic acid) and poly(ethyleneimine) andsold under the trade name SOLSPERSE 24000. This solid phase dispersingagent has a high binding affinity for the surface of the γ-iron oxide.It is believed that primary and secondary amino groups present in thedispersing agent provide this high binding affinity. Residual primaryand secondary amino groups present in the dispersing agent are alsobelieved to react with the epoxy group of the glycidyl methacrylate,while the vinyl groups from the methacrylate react with polymerisingradicals to become covalently bound to the polymer matrix. All of thecomponents of the organic phase are preferably pre-mixed in a separatetank and dispersed in water in the reaction tank. Once thepolymerisation reaction is substantially complete, the resultantpolymeric beads are subsequently reacted with an amine compound such aspiperidine or N,N-diethylethylenediamine or their respective salts toproduce a complexing resin. Reaction with the amine compound may bepromoted or accelerated by heating.

In another aspect, the present invention provides a process whichproduces polymeric beads of complexing resin incorporating magneticparticles which further incorporate a toughening agent. The tougheningagents are selected to increase the impact resistance of the resin.General techniques for increasing toughness of polymer materials may bereadily employed in the process of the present invention to affordpolymeric beads with increased durability. For example, rubbertoughening agents may be used to improve the strength and durability ofglycidyl methacrylate-based polymeric beads. The use of these rubbertoughening agents is believed to result in improved durability and anincreased service life of the polymeric beads. The rubber tougheningagents include low molecular weight rubbers which may be incorporatedinto the dispersed phase. A particularly preferred rubber tougheningagent is sold under the trade designation Kraton D1102 although othercommercially available rubber toughening agents can be used.

In another aspect, the present invention provides a method of separatingtransition metal ions from an aqueous solution comprising contactingsaid solution with polymeric beads of complexing resin according to thepresent invention. The metal-loaded beads may then be magnetised,causing them to aggregate and settle out of the treated solution.Alternatively, they can be separated on a wet high intensity magneticseparator or magnetic drum separator or similar device.

As mentioned above the polymeric beads of complexing resin of thepresent invention are preferably macroporous. The particle size of thepolymeric beads is preferably within the range of 30 μm to 1000 μm. Theparticles of solid material may have a particle size in the range ofsub-micron (e.g. 0.1 μm) to 500 μm and more preferably from 0.1 μm to 10μm.

The dispersing agent is a chemical compound or species that can reactwith at least one of the monomers used to produce the polymer matrixsuch that the dispersing agent is covalently bound within the polymermatrix. Further, the dispersing agent should have a good affinity forthe surface of the magnetic particles and preferably should be able tochemically bond to the surface of the magnetic particles. The use ofsuch an agent allows the magnetic particles to be dispersed throughoutthe polymer matrix.

As the magnetic particles are dispersed throughout the polymeric beadsof the present invention, the magnetic particles are not easily removedfrom the beads and this allows the beads to be subjected to a number ofhandling operations, such as conveying, pumping and mixing, withoutsubstantial erosion of solid particles therefrom.

The invention will be further described with reference to the followingnon-limiting Examples.

EXAMPLE 1 Preparation of Piperidine Functionalised Magnetic MacroporousComplexing Resin

Magnetic macroporous complexing resins were prepared in accordance withthe process of the present invention using the following raw materials:

-   1. Water: this is the continuous medium in which the organic phase    is dispersed and then reacted.-   2. Gohsenol® GH 20 (available from Nippon Gohsei) this is a high    molecular weight polymeric surfactant, a polyvinyl alcohol, that    disperses the organic phase in the water as droplets.-   3. Kraton D1102 (available from Shell Chemical Company): this acts    to improve the strength and durability of the resin.-   4. Cyclohexanol: this is the major porogen: it is a solvent for the    monomers, but a non-solvent for the polymer, and it promotes the    formation of voids and internal porosity in the resin beads.-   5. Toluene: this is the minor porogen.-   6. Solsperse® 24000 (available from Avecia Pigments & Additives): it    is a solid phase dispersing agent and is a block copolymer of    poly(hydroxystearic acid) and poly(ethyleneimine).-   7. Pferrox® 2228HC γ-Fe₂O₃ (available from Pfizer): gamma-iron oxide    (maghemite). This is the magnetic oxide that makes the resin beads    magnetic.-   8. DVB-50 (divinyl benzene): this is the monomer that crosslinks the    beads.-   9. GMA (glycidyl methacrylate): this monomer is polymerised to form    part of the polymer matrix. The polymerised residue of the monomer    provides epoxy groups within the matrix that can be subsequently    reacted to produce a complexing resin as follows:

-   10. VAZO® 67 (available from Dupont): this is the polymerisation    initiator, which activates when the mixture is heated above 75° C.-   11. Piperidine: this is the amine that reacts with the epoxy group    provided by the polymerised residue of glycidyl methacrylate to form    complexing groups.-   12. Ethanol: this is used as a rinse and as a wetting agent.    Method

Toluene (1.4 kg), cyclohexanol (5.5 kg) and Solsperse 24000 (2.5 kg)were charged to a mix tank. The solution was then stirred slowly with aCowles-type dispersing blade while Pferrox 2228 HC γ-Fe₂O₃ (13 kg) wasadded. The speed was increased and held for a time sufficient to breakup the large aggregates. This mix was then passed through a closed-headbead mill with sufficient residence time to ensure that the majority ofthe particles were smaller than 5 μm in size. In a separate mix tank,toluene (2.6 kg), cyclohexanol (1.6 kg) and Kraton D1102 (1 kg) wereadded and stirred until the rubber had dissolved. The solution of rubberwas then added to the pigment dispersion and mixed until it washomogeneous.

Water (110 L) was charged to a 250 L reactor and the stirrer andnitrogen purge started. Next Gohsenol® GH-20 (400 g) was added, and thewater phase heated to 80° C. to dissolve the surfactant. While the waterwas heating the prepared pigment and rubber solution was charged to aseparate stirred mix tank and the stirrer turned on. Glycidylmethacrylate (21 kg), divinylbenzene (5.2 kg) and cyclohexanol (14 kg)were added in turn. A solution of Vazo 67 (100 g) in toluene (100 g) wasthen added, and the mixture was stirred for a further five minutesbefore adding it to the heated water phase. The resulting dispersion washeld at 80° C. (±5° C.) for two hours, during which time polymerisationoccurred and solid resin beads (44 kg) were formed.

The resultant beads contained 25% by weight of γ-Fe₂O₃ and had a meanparticle diameter of 225 μm, with a standard deviation of 100 μm. Aportion of this resin was cleaned of the excess γ-Fe₂O₃ and organicsolvent by repeated cycles of washing, settling and decanting. 50 mL (16g) of this resin was then slurried in 100 mL of water and heated to 85°C. Piperidine (6.8 g, 80 mmol) was added and the mixture heated at 85°C. under nitrogen for four hours. The beads were then washed and asample dried under vacuum at 60° C. and weighed. Wet resin was treatedsuccessively with 1 M sodium chloride solution acidified to pH 1; water;0.2 M potassium nitrate solution; water; 0.1 M sodium hydroxidesolution; water; neutral 1 M sodium chloride solution; water; 0.2 Mpotassium nitrate solution. The chloride ions displaced by potassiumnitrate were titrated with silver nitrate, yielding a total capacity of2.11 meq/g and a strong base capacity of 0.10 meq/g. The weak basecapacity is therefore 2.01 meq/g.

The maghemite was well dispersed throughout the resin beads produced inthis Example.

EXAMPLE 2 Preparation of N,N-diethylethylene Diamine FunctionalisedMagnetic Macroporous Complexing Resin

Magnetic macroporous complexing resins were prepared in a similarfashion to Example 1, except the solid resin beads (16 g) were aminatedwith N,N-diethylethylene diamine (DEDA, 9.3 g, and 80 mmol) instead ofpiperidine.

EXAMPLE 3 Evaluation of Copper Uptake as a Function of pH by ComplexingResin Prepared in Example 1

The complexing performance of resin prepared in Example 1 was assessedby measuring copper uptake as a function of pH. The resin sample wastreated with 1 M sodium hydroxide solution to ensure that weak basegroups were in the free base form, then rinsed with water. Samples wereequilibrated with copper (II) sulfate solutions initially containing 0.5mmol Cu(II) per meq of weak base capacity and ranging in pH from 2 to 5.The uptake of copper varied from 0.17 mmol per gram of resin at pH 2 to0.43 mmol/g at pH5 as shown in Table 1. (At higher pH copper hydroxideprecipitated).

TABLE 1 pH Copper Uptake (mmol/g) 2 0.17 3 0.18 4 0.34 5 0.43

EXAMPLE 4 Evaluation of Copper Uptake by Complexing Resin Prepared inExample 2 in the Presence or Absence of MgSO₄

The complexing performance and chelate selectivity of the resin preparedin Example 2 was assessed by measuring copper uptake as a function ofcopper concentration, in solutions with and without magnesium sulfate.The resin was treated with 1 M NaOH and rinsed. Samples were thenequilibrated at pH with CuSO₄ having initial concentrations ranging from1 to 40 mM. The experiment was repeated with a second series of CuSO₄solutions, which also contained magnesium sulfate at a concentration of27 mM. The uptakes of copper in the two experiments were very similar,reaching approximately 0.22 mmol/g at equilibrium CuSO₄ concentrationsabove 13 mM (Table 2). More than 90% of the adsorbed copper was desorbedin about 15 bed volumes of 0.1 M hydrochloric acid. The required volumeof acid decreases with increasing acid concentration, with slight lossesof iron oxide from the beads at high concentration.

TABLE 2 Copper Concentration Copper Uptake no Copper Uptake with(mmol/L) MgSO₄ (mmol/g) MgSO₄ (mmol/g) 0.01 — 0.03 0.06 0.08 — 0.07 —0.11 0.12 0.05 — 0.18 — 0.08 0.20 — 0.135 0.31 0.125 — 2.74 0.195 — 3.42— 0.19 11.0 0.23 — 13.4 — 0.225 28.6 0.26 —

EXAMPLE 5 Evaluation of Zinc and Cadmium Uptake by Complexing ResinsPrepared in Examples 1 and 2

The uptake of zinc and cadmium by resins prepared in Examples 1 and 2were evaluated. The resins from Examples 1 and 2, after treatment with 1M NaOH solution, were equilibrated with zinc sulfate and cadmium sulfatesolutions having initial concentrations ranging from 1 to 40 mM. At pH 6and equilibrium ZnSO₄ concentrations about 6 mM the piperidine resinadsorbed 0.22 and the DEDA resin 0.3 mmol Zn/g. Maximum cadmium uptakeswere 0.29 and 0.35 mmol/g. Both resins were more than 90% regeneratedwith 12-18 bed volumes of 0.1 M HCl.

EXAMPLE 6 Comparison of the Uptake Rate of Complexing Resins Prepared inExamples 1 and 2 with a Commercial Complexing Resin

The uptake rates of resins prepared in Examples 1 and 2 were evaluatedand compared with values obtained using a commercial polyaminecomplexing resin (Fuji PEI-CS-07). Resins from Example 1 and 2 (40 mL),after treatment with 1 M NaOH solution, were suspended in 50 mL of waterwith continuous stirring and CuSO₄ or CdSO₄ (0.5 mol per mol of weakbase group) added. The disappearance of metal ions was monitored as afunction of time. For comparison the copper uptake experiments wererepeated with the commercial polyamine resin Fuji PEI-CS-07. Thepiperidine-functionalised resin removed 50% of the added copper in 30seconds at pH 5 and essentially all of it in less than 50 minutes (Table3). Uptake of cadmium at pH 6 reached 50% in about 15 seconds and 95%after about 45 minutes (Table 4). Uptake of copper on theDEDA-functionalised resin at pH 5.4 reached 50% in less than 30 secondsand essentially 100% in less than an hour (Table 5). In contrast, thecommercial resin adsorbed only 35% of the copper in one hour and had notreached equilibrium after 72 hours (Table 6).

TABLE 3 Fraction of Copper Remaining Time (min) ([Cu]/[Cu]₀) 0 1 1 0.2125 0.176 10 0.061 15 0.049 30 0.017 45 0.00

TABLE 4 Fraction of Cadmium Time (min) Remaining ([Cd]/[Cd]₀) 0 1 50.101 10 0.088 30 0.060 45 0.055 60 0.041

TABLE 5 Fraction of Copper Time (min) Remaining ([Cu]/[Cu]₀) 0 1 1 0.195 0.10 10 0.077 15 0.039 30 0.019 45 0.015 60 0.007 120 0.010 300 0.007430 0.002

TABLE 6 Fraction of Copper Time (min) Remaining ([Cu]/[Cu]₀) 0 1 5 0.9210 0.82 15 0.87 30 0.74 45 0.68 60 0.64 120 0.56 210 0.53 1200 0.59

It will be appreciated that the invention described herein issusceptible to variations and modifications other than thosespecifically described. It is to be understood that the inventionencompasses all such variations and modifications that fall within thespirit and scope.

Throughout this specification and the claims which follow, unless thecontext requires otherwise word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

1. Polymeric beads of complexing resin comprising a polymer matrixhaving magnetic particles and a dispersing agent dispersed substantiallyuniformly therein, wherein the polymer matrix incorporates amine groupsthat are complexed with transition metal cation.
 2. The polymeric beadsof claim 1, wherein the dispersing agent is covalently bound within thepolymeric matrix.
 3. The polymeric beads of claim 1 prepared by aprocess which comprises: (a) producing a dispersion having a continuousaqueous phase and a dispersed organic phase, said organic phasecomprising one or more polymerizable monomers, magnetic particles and adispersing agent for dispersing said magnetic particles in the organicphase; polymerizing said one or more polymerizable monomers to formpolymeric beads incorporating said magnetic particles, wherein saidpolymeric beads include amine groups that are capable of complexing atransition metal cation and that are provided by polymerized residues ofsaid one or more polymerizable monomers, or wherein said polymeric beadsare reacted with one or more compounds to provide amine groups capableof complexing a transition metal cation; and (b) contacting theso-formed polymeric beads with an aqueous solution comprising transitionmetal cations such that the amine groups of the beads complex withtransition metal cations.
 4. The polymeric beads according to claim 3wherein the organic phase comprises two or more monomers.
 5. Thepolymeric beads according to claim 3 wherein said one or morepolymerizable monomers are selected from: (a) crosslinking monomerswhich are able to provide crosslink points; and (b) functional monomerswhich are able to provide functional groups.
 6. The polymeric beadsaccording to claim 5 wherein said functional monomer provides aminegroups capable of complexing a transition metal cation.
 7. The polymericbeads according to claim 6 wherein said functional monomer providesamine groups selected from dimethylaminoethyl methacrylate, aminopropylacrylamide and methacrylamide, N,N-dimethylaminopropyl acrylamide andmethacrylamide, vinyl pyridine, organic-soluble diallylamine andvinylimidazole salts.
 8. The polymeric beads according to claim 5wherein said functional monomer includes a functional group capable ofreaction with one or more compounds to provide said amine groups capableof complexing a transition metal cation.
 9. The polymeric beadsaccording to claim 8 wherein said functional monomer capable ofproviding amine groups includes an amide group.
 10. The polymeric beadsaccording to claim 9 wherein said functional monomer including an amidegroup is selected from N-vinyl formamide and N-methyl-N-vinyl acetamide.11. The polymeric beads according to claim 8 wherein said functionalmonomer capable of providing amine groups includes an epoxy group. 12.The polymeric beads according to claim 11 wherein said functionalmonomer including an epoxy group is glycidyl methacrylate.
 13. Thepolymeric beads according to claim 8 wherein said functional monomercapable of providing amine groups is a vinyl ester.
 14. The polymericbeads according to claim 13 wherein said vinyl ester is selected fromacrylate and methacrylate esters.
 15. The polymeric beads according toclaim 14 wherein the acrylate ester is methyl acrylate.
 16. Thepolymeric beads according to claim 3 wherein said one or morepolymerizable monomers further includes one or more back bone monomers.17. The polymeric beads according to claim 3 wherein said dispersedorganic phase further comprises a porogen.
 18. The polymeric beadsaccording to claim 1 wherein the magnetic particles are selected fromγ-iron oxide, magnetite and chromium dioxide.
 19. The polymeric beadsaccording to claim 3 wherein the dispersion is stabilized using astabilizing agent.